pick method
Opens the system ringtone picker and returns the selected ringtone URI.
existingUri - Optional URI to pre-select in the picker.
Returns null if the user cancels.
Implementation
Future<String?> pick(RingtoneType type, {String? existingUri}) =>
_invoke<String>('ringtones.pick', {
'type': type.name,
'existingUri': ?existingUri,
});